Almost all modern
machinery makes some use of gears as
a medium for transmitting power. Such use
may be for the purpose of either
changing the speed of a driven member
or changing the direction of movement. In
either case the gears act as a lever so
that , in most cases, the force transmitted
is multiplied and in so doing speed
will be reduced. When variations in the
torque or speed transmitted are desired, a
series of gear ratios can be provided
in the same mechanism.
Most gear sets
are lubricated with fluid products or
gear oils, and consequently, such compounds will
receive major consideration . Since plastic or
semi-fluid products, such as lubricating greases,
as well as solids are sometimes used
as gear lubricants, they will also receive
mention.
It is also
the purpose to describe fluids employed
in certain fluid drives, particularly automatic
transmissions in automotive vehicles. Here the
oils in question serve a number of
functions, and it is necessary that a
single fluid satisfy not only lubrication
of different mechanisms, but also act as
a torque converter and hydraulic agent.
This is simply
an extension of the functions which
gear oils fill in many case. Thus, gear
lubricants also take care of bearing lubrication in many
applications. It will be presumed that most
readers are familiar with the mechanisms to
be lubricated, such as automatic transmissions,
hypoid gears, worm gears, etc. Therefore, little description of
mechanical details will be attempted.
The primary
interest will be in lubricants for
metal gears, although mention will be made
of the requirements for gears made
from other materials. An attempt will be
made to thoroughly explain how
lubricants for gears function, what they contain,
how they are compounded, and the
limitations of their use. In all of
this it should be kept in mind
that to be most effective any
lubricant should be applied in the
right amount at the right place and
the right time.
Fundamentally the
types of motion in operating gear
sets are those occurring in other
machine elements , namely, rolling and sliding motion.
The two types of movement may occur simultaneously as in
meshing hypoid gears. This is pointed out
so that it will be realized that,
even though the configuration of gears
differ from bearings, the lubricating
problems are similar for both mechanisms. Another
point to keep in mind is that
while the title of the mentions both
gear and transmission lubrication, the latter
mechanism is most often one or
more gear sets serving a specific purpose.
Therefore, except in the case of fluid
drives, the problem is one of gear
lubrication. Finally , some of the possibilities of
future trends and developments in gear
lubricants and torque fluids will be
mentioned.
